Generally, there exist various pollutants and total phosphor (T-P) in raw and sewage water, wastewater and rain water, especially which have high phosphorus loading.
For that reason, the phosphor as nutrients flowed into a water discharging area causes large amounts of algae around eutrophicated waters, having an adverse effect on the ecosystem of aquatic lives.
To remove suspended solid (hereinafter, SS) or phosphor and the like, raw water that contains pollutants and phosphor has been treated with chemicals to form floc particles to be processed by flocculation and precipitation.
For this process, large scale processing facilities such as a service water supply or a sewage disposal plant are equipped with a coagulation tank, a flocculation tank and a precipitation tank separately, which requires a large space for facilities and has great difficulties in operating and managing thereof.
Moreover, a traditional sewage water treatment device is designed to use various filtration media such as sand and the like to remove pollutants such as insoluble SS and T-P, and decrease biological oxygen demand (BOD) more effectively.
However, the amount of pollutants flowed into a sewage treatment device varies depending on the velocity of flow and the flux of sewage water, which results in ineffective filtration process. In addition, fluctuations in head loss occurred in the filtration media and in the filtration processing time requires backwashing on a regular or irregular basis, causing a difficulty in setting a backwashing cycle.
If backwashing is not performed properly in the conventional high speed filtration device, filtration efficiency is greatly reduced. Further, the conventional method of backwash is designed to supply backwash water constantly such that the water overflows the filtration device to discharge pollutants along with the backwash water requiring substantial amount of backwash water consumption. Another problem for this process is that the backwash water needs to be filtered in another sewage treatment process as well.